Background: Many studies have shown that programmed cell death protein 1 (PD-1) and its ligand, PD-L1, are expressed in advanced gastric cancer. Furthermore, detection of these proteins is associated with infiltrating CD8+ T-cells, indicating that an adaptive immune resistance mechanism occurs in advanced gastric cancer. However, PD-L1 and PD-1 expression in gastric intraepithelial neoplasia and early-stage gastric cancer (EGC) has yet to be elucidated. Patients and methods: Fifty-four resections of low-grade intraepithelial neoplasia (LGIN), high-grade intraepithelial neoplasia (HGIN), and EGC were stained by immunohistochemistry for PD-1, PD-L1, and CD8. CD8+ T-cell densities both within tumors and in the tumor-stromal interface were analyzed. Flow cytometry (FACS) was used to analyze the PD-1 expression in tumor tissues and peripheral blood mononuclear cells. Furthermore, the relationship between Helicobacter pylori (Hp) infection and PD-1 and PD-L1 was also evaluated. Results: We demonstrated that PD-L1 expression was significantly increased in HGIN and EGC compared with LGIN, and both PD-1 and PD-L1 showed similar expression patterns, being mainly detected in infiltrating immune cells. FACS also showed that PD-1 was expressed on both CD4+ and CD8+ T-cells. However, no difference was found in CD8+ T-cell infiltration between LGIN and HGIN+EGC, and this was not not found to be associated with PD-L1 or PD-1 expression. However, Hp infection was significantly associated with expression of PD-L1 and PD-1. Conclusions: The PD-1/PD-L1 checkpoint is involved in intraepithelial neoplasia and EGC, but an adaptive immune resistance mechanism does not occur. Expression of PD-1/PD-L1 is also associated with Hp infection, and so Hp infection may be an important initiating factor. Clinical Trial Registration information: This study was approved by the Institutional Review Board of Ruijin Hospital and written informed consent was obtained from all patients.

Oxidative stress and the production of reactive oxygen species (ROS) are a biological threat to bacteria, which induce the synthesis of proteins and production of antioxidants to combat it. Herein, we report that glutamate dehydrogenase (GDH) of Salmonella can assimilate ammonium into glutamate and promote the generation of glutathione (GSH) to combat oxidative damage. Oxidation induces the transcription of gdhA, which encodes GDH, and activates the enzymatic activity of GDH. The DgdhA mutant Salmonella strain showed decreased levels of GSH and reduced survival in macrophages, and this growth deficiency could be partially restored by overexpression of GDH and complementation with its downstream metabolites. Therefore, GDH plays a critical role in the growth of Salmonella in oxidative environments, especially under low energy supply.